1. Field of the Invention
This invention relates generally to piles, and particularly to precast reinforced concrete screw-threaded piles. This invention further relates to concrete piling constructed in sections to permit variations in the length of the piles.
2. Description of the Prior Art
In areas such as New Orleans, La. and adjacent parishes, or in soft and marshy lands which exist in places other than La., it is necessary to employ piles to provide a proper foundation for buildings and similar structures. Most commonly employed for residential and light commercial construction are friction piles usually constructed of wood. These piles may run 20 to 25 feet in length and must be driven into the ground by special machinery of large size. Accordingly, where such machinery is inaccessible, property owners have been unable to undertake desired construction.
A problem encountered with the use of precast concrete screw-threaded piling is encountered during handling of the piling between the manufacturing facility and site where the piling is to be used. Further, the length requirements for the piling varies as a function of the depth required at a particular site. Thus, it has generally been necessary in the past to construct such precast piling in a great variety of lengths in order to provide piling only of the length necessary for a particular application.
Another problem encountered with precast concrete screw-threaded piling is attainment of adequate strength at the threaded peripheral portions of the piles. This problem becomes more acute the deeper and closer together are the threads of the piles. While U.S. Pat. No. 1,563,024, issued Nov. 24, 1925, to G. Grimaud, discloses a reinforced concrete stake which employs shallow, widely spaced screw-threads formed on the outer surface of a concrete body and reinforced by a spiral binding wire wrapped around a framework extending parallel to the core of the stake, this construction is limited as to the depth of threads which may be employed due to the necessity of keeping the framework on which the binding wire is wound spaced a predetermined minimum distance from the bottom surfaces of the threads.
It is particularly desirable in order to construct a precast concrete screw-threaded piling which can be efficiently threaded into the earth, and the like, even by the use of an installer's hands, to have the screw-threads of the piles as deep and as close together as possible. The problem arises, however, of providing suitable reinforcement for such deep and closely spaced screw-threading.
A further problem experienced in prior art devices, is that the tensile and torsional stresses developed during the insertion of a concrete pile into the earth cannot be carried by concrete. It is known in the art, that concrete has great compressive strength, but has little or no tensile strength and little or no torsional strength. Thus, it has been a problem with prior art devices that the piling were not properly reinforced from the point of attachment of a suitable torsional driving force throughout the pile. Thus, the piling of the prior art would not be suitable for driving, because torsional stress would cause the concrete portion of the pile to fail. The following is a table of some prior art devices which have been patented.